1. Field of the Invention
The present invention relates to a laminated variable resistor, and more particularly to a laminated variable resistor with an active region of a metal phase.
2. Description of the Prior Art
The conventional laminated variable resistor, as shown in FIGS. 1A and 1B, includes a main body 10, internal electrodes 101, 102, 103 extending along two side edges of the main body into the main body 10, terminal electrodes 20 disposed on two ends of the main body, and a cover layer 30 disposed on the top surface of the main body. The main body mainly includes zinc oxide (ZnO) of more than 90 mole % mixed with a metal oxide of less than 10 mole % as an additive, wherein the metal constituting the metal oxide includes cobalt (Co), manganese (Mn), bismuth (Bi), stibium (Sb), chrome (Cr), nickel (Ni), titanium (Ti), stannum (Sn), lanthanum (La), neodymium (Nd), praseodymium (Pr), barium (Ba), magnesium (Mg), cerium (Ce), and boron (B). The aluminum nitrate (Al2(NO3)X), glass, silicon dioxide (SiO2) are used as a flux, and a metal selected from gold (Au), silver (Ag), palladium (Pd), platinum (Pt), rhodium (Rh), or the alloy of any two of such metals is used for the internal electrodes 101, etc.
The overlapping regions A, B, C between the opposite internal electrodes 101 and 102, 103 and 104 of the above conventional laminated variable resistor are “active regions” which function as a variable resistor and also have a characteristic of capacitor. In the structure of the active region shown in FIG. 2, zinc oxide (ZnO) grains 1001, are densely scattered between the overlapping regions of the internal electrodes 101 and 102, 102 and 103, 103 and 104, and the grain boundary 1002 in the periphery of the grains are filled with the oxide of a metal selected from cobalt (Co), manganese (Mn), bismuth (Bi), stibium (Sb), chrome (Cr), nickel (Ni), titanium (Ti), stannum (Sn), lanthanum (La), neodymium (Nd), praseodymium (Pr), barium (Ba), magnesium (Mg), cerium (Ce), boron (B), and rhodium (Rh).
According to the above description, the material in the active regions of the conventional laminated variable resistor is a metal oxide or a combination of a metal oxide and glass without having any metal phase, so that the breakdown voltage is high. Further, when the conventional laminated variable resistor is fabricated to be thin, it can only bear the current of low intensity. If the current is high, or an inrush current or a spark exists, the conventional laminated variable resistor may be burnt out. Moreover, the conventional laminated variable resistor has the disadvantages that the equipment for manufacturing the above conventional laminated variable resistor is expensive, and the working staff must be well trained. To train the staff takes a lot of time and is difficult.
In view of the above disadvantages of the conventional laminated variable resistor, the inventors did research for a long time and proposed an improvement directed at eliminating the above disadvantages.